Transmission Dynamics of the Withering Syndrome Rickettsia-like Organism to Abalone in California

Abstract

A sentinel study was conducted to investigate the distribution of the withering syndrome (WS) pathogen by deploying modules containing live red abalone at two different field sites, one near an onshore commercial abalone farm and one in proximity to wild aggregations of abalone, both in Southern California. A newly validated quantitative polymerase chain reaction (qPCR) assay was used to quantify the withering syndrome rickettsia like organism (WS-RLO) DNA in water, tissue and fecal samples. In addition, histological screenings were conducted on tissues from all surviving abalone to understand clinical infections of the pathogen. WS-RLO DNA copies were detected in modules at the wild site but not at the site off of the abalone farm (even though WS-RLO DNA was detected in the farm’s effluent; p > 0.05). Overall, proportions of clinical infections and WS-RLO DNA at both sites were very low and similar between sites (p > 0.05). Abalone infection prevalence and intensity of the WS-RLO was independent of WS-RLO DNA copy density in seawater. This study demonstrated the use of caged sentinel abalone to monitor RLO transmission in the field. The results of this study will help managers better understand the risk of infection of abalone exposed to the WS-RLO in situ.